Chip (die, integrated circuit) is one of the most import hardware foundations of modern electronic devices. For different chips to interchange information (including data, messages and commands, etc) following a same interface standard, a chip includes a transmitter circuit which is coupled to an associated receiver circuit of another chip via circuit board and/or transmission line(s). The transmitter circuit carries information in electric signal which is then sent to the receiver circuit; as the receiver circuit receives the signal, the receiver circuit retrieves the carried information from the received signal. For example, Ethernet network, optical fiber network, XAUI (10 Gigabit Media Independent Interface), PCI-E (Peripheral Component Interconnect Express) and SATA (Serial Advanced Technology Attachment) are commonly adopted interface standards of modern high-speed chip.
To ensure that receiver circuit can correctly retrieve information from the received signal, interface standard includes specifications which should be satisfied by receiver circuit, such as sensitivity to voltage level of the received signal, etc. By monitoring eye diagram of signal receiving of a receiver circuit, one can not only find whether the receiver circuit satisfies the specifications, but also reveal further behavior information of the receiver circuit, such as whether parameters of the receiver circuit are properly set. Therefore, correctly monitoring eye diagram of receiver circuit has become a key point of modern chip design.
An eye diagram of a receiver circuit extends along two axes of time and level (e.g., voltage level). For a received signal of a certain level, if a receiver circuit correctly retrieves information from the received signal by sampling based on a triggering of a certain phase (associated with a triggering time), the level and the triggering time are included into an eye range. On the other hand, if a certain level and a certain triggering time (phase) are not covered by the eye range, it means that the receiver circuit can not correctly retrieve information from a received signal of the level by sampling the received signal based on a phase associated with the triggering time.
In a prior art, monitoring eye diagram for a receiver circuit of a chip is achieved by using a test equipment to send a test signal to the receiver circuit, and manually adjusting the level and the triggering time (phase) of the received signal of the receiver circuit; information accordingly retrieved from the received signal is hence outputted by a transmitter circuit of the chip, and is compared with the original information embedded in the test signal to check if the two match. By systematically changing level and triggering time (phase) of the received signal of the receiver circuit, testing staff scans to obtain the eye diagram of the receiver circuit.
However, the prior art suffers from low degree of automation, consumes considerable human resource and hardware cost, and requires a longer duration to scan eye diagram. While comparing the original information and the retrieved information obtained based on a given level and a given triggering time (phase), a statistically meaningful eye diagram scan result for the given level and the given triggering time is preferably obtained by repeatedly comparing multiple contents of the original information and the retrieved information during the given level and the given triggering timing are constantly maintained. Nevertheless, owing to low automation of the prior art, such repetition of comparison has to be manually monitored by the testing staff, and consequently costs more human/hardware resources.
Besides, while outputting the retrieved information of the receiver circuit, signal receiving and recovery operations of the receiver circuit are not correctly reflected. As modern interface standard adopts embedded clock, information and associated clock are carried in a same signal; hence, when a receiver circuit receives a signal, it performs clock and data recovery (CDR) to recover the clock associated with the original information from the received signal, and then retrieves information by sampling the received signal based on the recovered clock. Unavoidably, the clock recovered from the received signal suffers from jitters (i.e., disturbances of clock period); thus, jitter characteristics are considered as one kind of performance for evaluating a receiver circuit. However, when the retrieved information of the receiver circuit is outputted based on the recovered clock of the receiver circuit, the outputted signal additionally suffers from jitters again, thus fails to correctly reflect actual operation of the receiver circuit, and hence degrades correctness of eye diagram scan.